R&S FSW Series User Manual

Measurements and Results
R&S
®
FSW
328User Manual 1173.9411.02 ─ 43
7.12 AM Modulation Depth Measurement
This measurement determines the AM modulation depth of an AM-modulated carrier.
● About the Measurement........................................................................................328
● AM Modulation Depth Results...............................................................................328
● AM Modulation Depth Configuration..................................................................... 329
● Optimizing and Troubleshooting the Measurement.............................................. 330
● How to Determine the AM Modulation Depth........................................................331
7.12.1 About the Measurement
The AM modulation depth, also known as a modulation index, indicates how much the
modulated signal varies around the carrier amplitude. It is defined as:
M
Depth
= peak signal amplitude / unmodulated carrier amplitude
So for M
Depth
= 0.5, for example, the carrier amplitude varies by 50% above and below
its unmodulated level, and for M
Depth
= 1.0 it varies by 100%.
When this measurement is activated, marker 1 is set to the peak level, which is consid-
ered to be the carrier level. Delta markers 2 and 3 are automatically set symmetrically
to the carrier on the adjacent peak values of the trace. The markers can be adjusted
manually, if necessary.
The R&S FSW calculates the power at the marker positions from the measured levels.
The AM modulation depth is calculated as the ratio between the power values at the
reference marker and at the delta markers. If the powers of the two AM side bands are
unequal, the mean value of the two power values is used for AM modulation depth cal-
culation.
7.12.2 AM Modulation Depth Results
As a result of the AM Modulation Depth measurement, the following values are dis-
played in the marker area of the diagram:
Label Description
MDepth AM modulation depth in percent
M1 Maximum of the signal (= carrier level)
D2 Offset of next peak to the right of the carrier
D3 Offset of the next peak to the left of the carrier
AM Modulation Depth Measurement

R&S FSW Series Specifications

General

Brand	R&S
Model	FSW Series
Category	Measuring Instruments
Language	English